Many electronic devices and systems include integrated circuits for the storage of data during the operation of the devices. For example, electronic devices such as computers, printing devices, scanning devices, personal digital assistants, calculators, computer work stations, audio and/or video devices, communications devices such as cellular telephones, and routers for packet switched networks may include memory in the form of integrated circuits for retaining data as part of their operation. Advantages of using integrated circuit memory compared to other forms of memory include space conservation and miniaturization, conserving limited battery resources, decreasing access time to data stored in the memory, and cutting the costs of assembling the electronic devices.
Dynamic Random Access Memory (“DRAM”) is an example of integrated circuit memory. DRAM typically comprises an array of semiconductor capacitor cells, each of which may hold an amount of electric charge that represents the logical value of a stored bit. The cells in the array are typically arranged in rows and columns. Each cell is defined by the intersection of a row and a column. Each cell in the DRAM array may be accessed by simultaneously addressing the intersecting row and column.
In operation, internal amplifiers in the DRAM sense the amounts of electric charges stored on the capacitors. Based on the sensed electric charges, the outputs of the sense amplifiers represent the logical values of the bits that are stored in the DRAM array. In this manner, the data stored in the array may be extracted from the DRAM integrated circuit for use by other integrated circuits in the electronic device. In addition, other internal circuitry on the DRAM refreshes the charges on those cells. In this manner, the DRAM compensates for leakages of electric charge from the semiconductor capacitor cells, such as leakage into the substrate of the DRAM integrated circuit. Such reading, writing, and maintaining of charge on the cells are substantial internal operations of the DRAM.
The DRAM integrated circuit also includes internal voltage generators that act as voltage sources for maintaining various parts of the DRAM integrated circuit at chosen voltage levels. The output voltage levels of the voltage generators are chosen to produce optimal performance of the DRAM integrated circuit by minimizing leakage of charge into the substrate of the integrated circuit and not crossing breakdown thresholds for the semiconductor structures in the integrated circuit.
If the internal voltage generators do not operate at their chosen voltage level, the DRAM integrated circuit may not operate efficiently or may fail. As the voltage sources are internal to the DRAM integrated circuit, there is presently no efficient method for monitoring these voltage generators to determine whether the integrated circuit is failing, has failed, or is operating inefficiently.